This application claims the priority of German Application No. 100 36 538.8 filed Jul. 27, 2000, which is incorporated herein by reference.
The invention relates to an optoelectronic apparatus having a transmitter that emits transmission light, a receiver that receives reflected light, and an evaluation unit, in which the transit time to of the transmission light that is guided in the monitored region and reflected back, as a reflected light, by an object is evaluated for determining the distance of the object.
An optoelectronic apparatus of this type is known from DE 43 41 080 C1. For locating objects in a monitored region, the optoelectronic apparatus has a transmitter that emits transmission light beams, and a receiver, which is embodied as a location-resolving detector and receives reflection light beams, the transmitter and receiver being integrated into a common housing. The transmission light beams are diverted by a diverting unit, and periodically guided inside a monitored region. A phase measurement is employed in determining the distance of objects in the monitored region. The phase measurement is used to determine the transit-time difference of the received reflection light beams reflected by an object relative to the transmission light beams emitted by the transmitter.
Outside of the monitored region, a test object is disposed inside the housing. For checking the function of the optoelectronic apparatus, the transmission light beams that the test object reflects back to the receiver as reflection light beams are evaluated in terms of their amplitude in an evaluation unit.
Thus, it is possible to verify whether the transmitter or receiver is functional. Disturbances caused by the aging or contamination of components can also be ascertained with the test measurement using the test object.
The test measurement using the test object is not, however, conclusive in terms of whether the distance measurement for locating the objects in the monitored region is error-free. The test measurement cannot eliminate errors that may occur in the distance measurement.
It is an object of the invention to embody an optoelectronic apparatus of the type mentioned at the outset to assure the highest possible precision and most reliable verification in objects in the monitored region.
The optoelectronic apparatus according to the invention accomplishes this object with the transmitter emitting the transmission light in the form of a sequence of transmission light pulses where a portion of the light quantity of a transmission light pulse is coupled out as a reference transmission light pulse and guided by way of a reference path to the receiver; and an evaluation unit determines the transit time tR of the reference transmission light pulse guided as a reference reflected light pulse to the receiver and the transit-time difference toxe2x88x92TR to determine the distance of an object.
That is, the optoelectronic apparatus of the invention has a distance sensor that operates according to the pulse-transit-time method. The distances of objects from the optoelectronic apparatus are ascertained through the determination of the transit time to of the transmission light pulses that are emitted by the transmitter and reflected, as reflected light pulses, by objects inside the monitored region onto the receiver of the distance sensor.
In accordance with the invention, a portion of the light quantity is coupled out, as a reference transmission light pulse, from the transmission light pulses, and guided to the receiver by way of a reference path.
In the evaluation unit of the optoelectronic apparatus, the transit time TR of the reference transmission light pulse that was guided as a reference reflected light pulse to the receiver is determined. Then, the transit-time difference toxe2x88x92TR is used to determine the distance of an object.
The primary concept of the invention, therefore, is to associate all of the distance measurements taken with the transmission light pulses with a reference measurement taken with the reference transmission light pulse. The length of the reference path is known in advance and, advantageously, stored in the evaluation unit.
The evaluation of the transit-time difference toxe2x88x92TR extensively eliminates internal measurement errors occurring in the distance measurement. One cause of such measurement errors is that the emission of a transmission light pulse does not occur simultaneously with the actuation of the transmitter due to a trigger pulse or the like. Instead, the transmission light pulse is emitted with a slight delay due to the finite transit times of the electrical signals in the individual components. These transit times exhibit variations as a result of fluctuations in temperature or operating voltage, or because of aging of the components.
The same is true for the registration of the reflected light pulses at the receiver. The conversion of the pulses into electrical reflection signals, and their amplification, is affected by delay times, which are likewise subjected to fluctuations caused by interfering influences.
In the ascertainment of the transit times to for determining the distance of objects in the monitored region, and the determination of the transit times TR in the reference measurement, the same delay times that are affected by fluctuations are superposed over the distance-measurement values. These disturbance-influenced delay times are eliminated in the formation of the transit-time difference toxe2x88x92TR, which considerably increases the precision and reproducibility of the distance measurement.
A particular advantage is that the referencing of the distance measurement is performed continuously for all of the transmission light pulses guided into the monitored region.
This advantage is also attained if a diverting unit periodically guides the transmission light pulses into the monitored region. Then, for creating a reference measurement for each diversion position of the diverting unit, a reference transmission light pulse is coupled out of a transmission light pulse that has been guided into the monitored region.
Another special advantage is that the coupling-out of the reference transmission light pulse does not limit the usable monitored region.
If the diverting unit is formed by a tilted mirror, for example, which periodically guides the transmission light pulses inside a full circle in an angular range of 0xc2x0 to 360xc2x0, no separate angular range need be reserved for the reference measurement. Rather, the entire angular range covered by the transmission light pulses is available for detecting objects.
A further essential advantage of the apparatus according to the invention is that the distance measurement within the entire monitored region is continuously monitored through the continuous referencing of the object detection by means of the reference measurements taken with the reference transmission light pulses.
Thus, the requirements for the use of the optoelectronic apparatus in the field of security technology and personnel safety can easily be met. A notable advantage is that, with the reference measurements taken in accordance with the invention, a multi-channel design of the components for determining the transit-time differences can be omitted.